Performance of a receiver in interfering conditions

ABSTRACT

A device  20  includes a receiver  21  for receiving and processing signals at least in a first frequency band and an antenna  216  which is connected to the receiver  21.  In order to improve the performance of such a receiver, the device  20  in addition includes a tuning component  217  for shifting a frequency response of the antenna  216  from the first frequency band to a second frequency band. Further, the device  20  includes a controlling portion  221  causing the tuning component  217  to shift the frequency response of the antenna  216  from the first frequency band to the second frequency band, in case a wideband noise is expected in the first frequency band. A corresponding method is shown as well.

FIELD OF THE INVENTION

The invention relates to a device comprising a receiver for receivingand processing signals and an antenna which is connected to thereceiver. The invention relates equally to a method for improving theperformance of such a receiver.

BACKGROUND OF THE INVENTION

Receivers for receiving and processing signals are well known in theart, for example in form of a GPS (Global Positioning System) receiverof a GPS system.

The performance of a receiver may be degraded during time intervals inwhich wideband noise in the frequency band used for the signals whichare to be received by the receiver is present in the environment of thedevice, since this wideband noise may reduce the signal-to-noise ratio(SNR) of the received signals significantly.

The wideband noise can be generated in particular by a communicationsystem transmitter integrated in the same device as the receiver, or bya nearby communication system transmitter external to this device. Suchan internal or external communication system transmitter can be forinstance part of a GSM (Global System for Mobile communications)transceiver, of a CDMA (Code Division Multiple Access) transceiver, of aUS-TDMA transceiver or of a WCDMA (Wideband CDMA) transceiver.

In a GPS system, for example, several GPS satellites that orbit theearth transmit signals which are received and evaluated by GPSreceivers. All GPS satellites use the same two carrier frequencies L1and L2 of 1575.42 MHz and 1227.60 MHz, respectively. GPS signaling isbased on a CDMA principle, i.e. the satellites and their signals areseparated by the codes used to modulate the two carrier signals. Theemployed carrier modulation is a BPSK (bi-phase shift key) modulation,in which the carrier frequency phase is shifted by 180 degrees everytime a chip changes from zero to one or vice versa.

The modulation of the carrier frequencies L1 and L2 is illustrated inFIG. 1. After a phase shift of 90 degrees, the sinusoidal L1 carriersignal is BPSK modulated by each satellite with a different C/A (CoarseAcquisition) code known at the receivers. Thus, different channels areobtained for the transmission by the different satellites. The C/A code,which is spreading the spectrum over a 1.023 MHz bandwidth, is apseudorandom noise sequence which is repeated every 1023 chips, theepoch of the code being 1 ms. The term chips is used to distinguish thebits of a modulation code from data bits.

In parallel, the L1 carrier signal is BPSK modulated after anattenuation by 3 dB with a P-code (Precision code), and the L2 carriersignal is BPSK modulated with the same P-code before an attenuation by 6dB. Before transmission, the two differently modulated parts of the L1carrier signal are summed again. The L2 carrier signal carries currentlyonly the P-code. The P-code is much longer than the C/A code. Its chiprate is 10.23 MHz and it repeats every 7 days. In addition, the P-codeis currently encrypted, and for that reason it is often referred to asP(Y)-code. Decryption keys needed for using the P(Y)-code are classifiedand civil users cannot access them. Therefore, only the L1 carrier C/Acode is usable in civil GPS receivers.

Before the C/A code and the P(Y)-code are modulated onto the L1 signaland the L2 signal, navigation data bits are added to the C/A andP(Y)-codes by using a modulo-2 addition with a bit rate of 50 bits/s.The navigation information, which constitutes a data sequence, can beevaluated for example for determining the position of the respectivereceiver. The navigation information comprises e.g. precise satelliteorbital parameters and clock correction parameters. When a receiver isable to despread a received signal based on the correct modulation code,it can extract and evaluate the navigation data. A GPS signal which isreceived at a GPS receiver is further modulated due to the Dopplereffect and possibly due other higher order dynamic stresses.

The reception bandwidth of a GPS receiver receiving the modulatedsatellite signals is related to the reception code. For example, if GPSis based on the L1 carrier C/A code, then the signal requires afrequency band of 1575.42 MHz+/−5 MHz. If a P-code capable receiver isused, then the reception band of the GPS receiver is much wider, it islikely to be 1575.42 MHz+/−24 MHz. The actual used GPS receptionbandwidth is further related to the actual implementation, and thus thepreviously mentioned bandwidths are presented for demonstrationpurposes. The mentioned GPS bandwidth will thus be used in the followingonly by way of example.

The GPS standard is currently under modernization. One of the maincomponents of the modernization consists in two new navigation signalsthat will be available for civil use in addition to the existingcivilian service broadcast of the L1-C/A code at 1575.42 MHz.

The first one of these new signals will be a C/A code located at 1227.60MHz, i.e. modulated onto the L2 carrier frequency, and will be availablefor general use in non-safety critical applications. The new civiliansignal at L2, referred to as “L2CS”, will generally be characterized bya 1.023 Mcps (mega chips per second) effective ranging code having aTime Division Multiplex of two ½ rate codes. The L2CS signal will beBPSK modulated onto the L2 carrier, along with the P(Y)-code. This C/Acode will be available beginning with the initial GPS Block IIFsatellite scheduled for launch in 2003.

The second one of the new signals will be using a third carrierfrequency L5 located at 1176.45 MHz. The L5 carrier frequency will bemodulated with C/A codes, more specifically with a CL code of 767,250chips and a CM code of 10,230 chips. The L5 signal will provide a 10.23Mcps ranging code, wherein it is expected that improved crosscorrelation properties will be realized. The L5 signal will be messagebased. It will include an I (In-phase) channel carrying 10-symbolNeumann/Hoffman encoding and a Q (Quadrature) channel carrying 20-symbolNeumann/Hoffman encoding. The I and Q channels will be orthogonallymodulated onto the L5 carrier. The L5 signal falls into a frequency bandwhich is protected worldwide for aeronautical radionavigation, andtherefore it will be protected for safety-of-life applications.Additionally, it will not cause any interference to existing systems.Thus, with no modification of existing systems, the addition of the L5signal will make GPS a more robust radionavigation service for manyaviation applications, as well as for all ground-based users, likemaritime, railways, surface, shipping, etc. The L5 signal will providesignificant benefits above and beyond the capabilities of the currentGPS constellation, even after the planned second civil frequency L2becomes available. Benefits include precision approach navigationworldwide, increased availability of precision navigation operations incertain areas of the world, and interference mitigation. The new L5signal will be available on GPS Block IIF satellites scheduled forlaunch beginning in 2005.

At the current GPS satellite replenishment rate, all three civilsignals, i.e. L1-C/A, L2-C/A and L5, will be available for initialoperational capability by 2010, and for full operational capabilityapproximately by 2013.

In particular communication systems operating in the 1900 band, likeGSM1900, which are widely referred to as PCS (Personal CommunicationSystem), and communication systems operating in the 1800 band, likeGSM1800, which are widely referred to as DCS (Digital CommunicationSystem), will generate wideband noise in this GPS L1 band of 1575.42MHz+/−5 MHz, when C/A code supported GPS is used. When new L2 and L5frequency GPS signals are used, then lower frequency GSM signals, i.e.GSM900 and-GSM800, will generate the same wide band noise problem asGSM1800 to the L1 GPS signal.

Measurements show that if no measures are taken, the SNR of a GPS signalreceived by a GPS receiver degrades by about 2 dB in case a GSMtransmitter implemented in the same device uses for transmissions asingle slot TX (transmission) mode, and by about 3 dB in case the GSMtransceiver implemented in the same device uses for transmissions a dualslot TX mode.

The GPS receiver, however, requires a sufficient SNR of receivedsatellite signals for being able to correctly acquire and track thesignal based on its C/A-code and thus to make use of its content. It isbetter for the performance of the GPS receiver to receive signals with aparticularly low SNR than not to receive any signal at all during shorttime intervals.

Typically in spread spectrum systems, the AGC (Automatic Gain Control)tunes the received information signal level for A/D (analog to digital)conversion based on the noise level. In normal operation conditions, thenoise is coming from background noise, which has a constant power level.The problem arises when the noise level rises rapidly and the AGC triesto adjust an incoming signal to a certain appropriate level for an A/Dconversion. A fast varying high noise level can cause saturation in theA/D converter and the amplitude of the signal is clipped. If the signalis clipped in conversion, some information signal is lost and thus thereceiver performance is degraded.

Also external interferences can block a GPS receiver operationcompletely, in case multiple communication system transmitters aretransmitting in the same area at the same time.

The same problem may further occur when a Galileo receiver is usedinstead of a GPS receiver. Galileo is a European satellite positioningsystem, for which the beginning of commercial operations is scheduledfor 2008. Galileo comprises 30 satellites, which are distributed tothree circular orbits to cover the entire surface of the Earth. Thesatellites will further be supported by a worldwide network of groundstations. It is planned that Galileo will provide ten navigation signalsin Right Hand Circular Polarization (RHCP) in the frequency ranges1164-1215 MHz, using carrier signals E5a and E5b, 1215-1300 MHz, using acarrier signal E6, and 1559-1592 MHz, using a carrier signal E2-L1-E1.Similarly as with GPS, the carrier frequencies E5a, E5b, E6 and E2-L1-E1will be modulated by each satellite with several PRN codes spreading thespectrum and with data. Thus, GSM transmitters may equally generatewideband interferences in frequency bands employed by Galileo.

Obviously, the performance of a receiver due to transmissions by acommunication system transmitter may equally be degraded in a similarsituation in case of another type of a communication system transmitterthan a GSM transmitter and/or another type of a receiver than a GPSreceiver or a Galileo receiver.

In U.S. Pat. No. 6,107,960, a method is proposed for reducingcross-interferences in a combined satellite positioning system receiverand communication system transceiver device. A control signal istransmitted from the communication system transceiver to the satellitepositioning system receiver, when the communication transceivertransmits data at a high power level over a communication link. Thecontrol signal causes the satellite positioning system signals fromsatellites to be blocked from the receiving circuits of the satellitepositioning system receiver, or to be disregarded by the processingcircuits of the satellite positioning system receiver.

For a communication system transmitter which is combined in a singledevice with the satellite positioning system receiver, it has furtherbeen proposed to improve the SNR of received satellite signals by addingan external notch-filter to the transmission path of the communicationsystem transmitter. The notch filter, which is arranged after a poweramplifier in the transmission path, has a passband frequency range forpassing on the frequencies required for the communication system, and astop band frequency range for attenuating the frequencies required forthe satellite positioning system.

For PCS and DCS, the passband frequency range of the notch filter has tobe 1710 MHz to 1910 MHz, and in case GPS is used as satellitepositioning system, the stop band frequency range has to be 1558.42 MHzto 1580.43 MHz. In order to improve the SNR of received GPS signals to auseful level, a very high attenuation is required for the stop band.Applying a high attenuation, however, increases also the insertion lossof the notch filter at the pass band of the filter. Due to thisadditional loss after the power amplifier, more output power has to betaken from the power amplifier, which increases the current consumption.

Measurements show that an antenna isolation of about 10 dB is requiredfor single slot GSM, if the GPS SNR is to be improved to a desired levelof 0.5 dB degradation. To a GSM1800 transmission path, a 30 dB externalGPS band attenuator has to be added for achieving the same desired levelof 0.5 dB degradation. For dual slot GSM, the required attenuation iseven higher.

The insertion loss of a GPS notch-filter with a 30 dB GPS bandattenuation will lie between 0.7 dB and 1.0 dB. An insertion lossbetween 0.7 dB and 1.0 db increases the current consumption of the poweramplifier by about 20%, compared to a current consumption withoutinsertion loss.

It is thus a disadvantage of the approach using a notch-filter that anextra component is needed in the communication system transmitter andthat the power amplifier current consumption increases about 20%, whichalso results in an increased heating of the device. On the whole, thecosts for improving the GPS SNR by only about 1.5 dB are high.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an alternative to existingsolutions for improving the performance of a receiver in interferingconditions.

On the one hand, a device is proposed, which comprises a receiver forreceiving and processing signals at least in a first frequency band, andat least a first antenna which is connected to the receiver. Theproposed device further comprises a tuning component for shifting afrequency response of the first antenna from the first frequency band toa second frequency band. The tuning component may include for instance acapacitance diode, but equally or any other suitable components.Moreover, the proposed device comprises a controlling portion causingthe tuning component to shift the frequency response of the antenna fromthe first frequency band to the second frequency band, in case awideband noise is expected in the first frequency band.

On the other hand, a method for improving the performance of a receiveris proposed. The receiver is able to receive and process signals atleast in a first frequency band, and it is connected to at least a firstantenna. The proposed method comprises as a first step determiningwhether a wideband noise is expected in the first frequency band. Theproposed method comprises as a second step shifting a frequency responseof the first antenna from the first frequency band to a second frequencyband, in case a wideband noise is determined to be expected in the firstfrequency band.

The invention proceeds from the consideration that some receivers, likeGPS receivers, have severe problems in coping with high noise levels. Itis therefore proposed that when wideband noise is generated in thefrequency band employed for the signals which are to be received by thereceiver, the antenna is detuned out of the regular center frequency. Asa result, the wideband noise cannot be received any more via the antennaand does thus not disturb the receiver.

It is an advantage of the invention that it provides an alternative toexisting solutions.

When detuning the antenna, also the received signal is attenuated. Ifthe received signal is weak, the attenuation causes that the signalcannot be detected. However, if the signal is strong, it may be possibleto detect the signal in spite of the attenuation. This constitutes anadvantage compared to the solution proposed in the above cited documentU.S. Pat. No. 6,107,960, as here, the blocking or disregarding ofsatellite signals affects satellite signals of any strength.

It is further an advantage of the invention that it requires noadditional components in a communication system transmitter of thedevice.

Preferred embodiments of the invention become apparent from thedependent claims.

The invention can be employed in any device comprising a receiver. Thereceiver can be for example a satellite positioning system receiver likea GPS receiver or a Galileo receiver, but equally any other type ofreceiver. The invention can be employed in particular, though notexclusively, in any device comprising a receiver and in addition acommunication system transmitter. The communication system transmittercan be for example part of a GSM transceiver, of a US-TDMA transceiver,of a WCDMA-GSM transceiver or of a CDMA transceiver.

In case the invention is employed in a device comprising in addition acommunication system transmitter, it can be used in particular forattenuating wideband noise generated by this communication systemtransmitter in the first frequency band. Wideband noise in the firstfrequency band can then be expected by the controlling portion at leastwhenever the communication system transmitter is known to betransmitting signals. The controlling portion may either be part of thecommunication system transmitter or receive a corresponding informationabout transmissions from the communication system transmitter. It has tobe noted, however, that the invention can equally be employed forattenuating wideband noise generated by a unit external to the device.

In an advantageous embodiment, the receiver comprises at least a firstreceiving chain for receiving and processing radio frequency signals inthe first frequency band and a second receiving chain for receiving andprocessing radio frequency signals in the second frequency band. In thisembodiment, the first antenna is connected to the first receiving chainand in addition via a switching component to the second receiving chain.The controlling portion can then cause the switching component toconnect the first antenna in addition to the second receiving chain,whenever a wideband noise is expected in the first frequency band.Thereby, the performance of the receiver can be improved, as signals maybe available for evaluation at the second frequency band while thesignals at the first frequency band are being disturbed by widebandnoise.

In case the receiver comprises two receiving chains, the deviceaccording to the invention comprises advantageously in addition a secondantenna, which has a frequency response at the second frequency band andwhich is equally connected via the switching component to the secondreceiving chain. The second antenna can be used for a diversityreception improvement in the receiver. The controlling portion may thencause the switching component to disconnect the second antenna from thesecond receiving chain, whenever the first antenna is connected via theswitching component to the second receiving chain since a wideband noiseis expected in the first frequency band.

In such a device, the controlling portion advantageously further causesthe switching component to connect the first antenna to the secondreceiving chain and to disconnect the second antenna from the secondreceiving chain, in case a wideband noise is expected in the secondfrequency band.

The noise in the second frequency band can be generated for example by asecond communication system transmitter of the device, which transmitssignals via a radio interface in a different frequency band than thefirst communication system transmitter of the device. In this case,wideband noise in the second frequency band can be expected by thecontrolling portion at least whenever the second communication systemtransmitter is known to be transmitting signals.

BRIEF DESCRIPTION OF THE FIGURES

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawing.

FIG. 1 illustrates the modulation of GPS carrier frequencies;

FIG. 2 is a schematic block diagram of a mobile phone, in which a firstembodiment of the invention is implemented;

FIG. 3 is a diagram illustrating the operation of the first embodimentof the invention;

FIG. 4 is a schematic block diagram of a mobile phone, in which a secondembodiment of the invention is implemented;

FIG. 5 is a diagram illustrating the operation of the second embodimentof the invention;

FIGS. 6 a and 6 b are a further diagrams illustrating the operation ofthe second embodiment of the invention;

FIG. 7 is a schematic block diagram of a mobile phone, in which a thirdembodiment of the invention is implemented; and

FIGS. 8 a and 8 b are diagrams illustrating the operation of the thirdembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a schematic block diagram of a mobile phone 20, in which afirst embodiment of the invention is implemented. Only selectedcomponents of the mobile phone 20 are depicted.

The mobile phone supports a GPS positioning and a mobile communicationvia a GSM network.

For supporting the GPS positioning, the mobile phone 20 comprises a GPSreceiver 21. The GPS receiver 21 includes, connected to each other inseries, a low noise amplifier LNA 211, a mixer 212, a variable gainattenuator 213 and a converters and DSP (digital signal processor)processor block 214. A local oscillator 215 is connected in addition tothe mixer 212. The local oscillator 215 provides a signal having afrequency required for downconverting an L1 signal. The mobile phone 20further comprises a GPS antenna 216 which is connected via a tuningcomponent 217 to the low noise amplifier 211 of the GPS receiver 21. Thetuning component 217 comprises a detuning circuitry, e.g. a capacitancediode, for tuning the frequency band which can be received via the GPSantenna 216.

For supporting the mobile communication, the mobile phone 20 comprises aGSM1800 transmitter 22, which is part of a GSM1800 transceiver. Thetransmitter 22 comprises, connected to each other in series, aconverters and DSP processor block 221, a first variable power amplifier222, a mixer 223 and a second variable power amplifier 224. Thetransmitter 22 further comprises a local oscillator 225, which isconnected to the mixer 223. The mobile phone 20 moreover comprises a GSMantenna 226, which is connected to the second variable amplifier 224.The converters and DSP processor block 221 of the transmitter 22 has acontrolling access to the tuning component 217.

A radio frequency signal reaching the mobile phone 20 is received by theGPS antenna 216, in case the signal lies within the frequency band ofthe frequency response of the GPS antenna 216. The tuning component 217is able to switch the frequency response of the GPS antenna 216 betweentwo different frequency bands, one of which is the GPS L1 frequencyband. A radio frequency signal received via the GPS antenna 216 isprocessed by the GPS receiver 21. More specifically, the received signalis amplified by the LNA 211 and mixed by the mixer 212 with a signalprovided by the local oscillator 215. In case the received signal is anL1 signal, the mixing results in a down-conversion to the base band. Thedownconverted signal is then attenuated or amplified by the variablegain attenuator 213 with a gain currently set by an AGC (automatic gaincontrol), and finally processed in a conventional way in the convertersand DSP processor block 214. The processing in the converters and DSPprocessor block 214 may comprise for instance determining and tracking aC/A-code in the signal, decoding a navigation information comprised inthe tracked signal and performing positioning calculations fordetermining the current position of the mobile phone 20.

A signal, which is to be transmitted by the GSM transmitter 22 in thescope of a mobile communication to a base station, is processed fortransmission in a conventional way by the GSM transmitter 22. The signalis provided by the converters and DSP processor block 221 to the firstvariable power amplifier 222, which amplifies the signal with acurrently set amplification factor. The amplified signal is then mixedby the mixer 223 with a signal provided by the local oscillator 225 foran up-conversion to a radio frequency signal. The radio frequency signalis further amplified by the second variable power amplifier 224 with acurrently set amplification factor. The amplification factors are set byan AGC according to a request by the base station of a communicationnetwork to which the mobile phone 20 is currently connected. The signaloutput by the second variable power amplifier 224 is then transmittedvia the GSM antenna 226.

The detuning of the GPS antenna 216 to another frequency band by thetuning component 217 will be explained in more detail in the followingwith reference to FIG. 3. FIG. 3 is a diagram which depicts on afrequency line the GSM1800 TX band of 1710-1785 MHz, the GPS L1 band of1570.30-1580.53 MHz, the GPS L2 band around 1227 MHz, the GPS L5 bandaround 1176.45 MHz and the GSM900 TX band of 880-925 MHz.

In a first state, the GSM transmitter 22 does not transmit any signals.In this first, basic state, the GPS antenna 216 is tuned by the tuningcomponent 217 to receive satellite signals in the GPS L1 frequency bandof 1570.30 MHz to 1580.53 MHz. The corresponding GPS antenna frequencyresponse is shown as a first curve in FIG. 3.

In a second state, the GSM transmitter 22 transmits signals having acarrier frequency in the range of 1710-1785 MHz, causing wideband noisein the GPS L1 frequency band of 1575.42 MHz+/−5 MHz. The distribution ofthe power level of transmitted GSM1800 signals over the frequency isdepicted as second curve in FIG. 3. The generated wideband noise issuperimposed on any satellite signal reaching the GPS antenna 216. Thewideband noise degrades the performance of the GPS receiver 21, in caseit reduces the SNR of received GPS L1 satellites signals below anacceptable value.

When the GSM transmitter 22 transmits signals with a power levelexceeding a predetermined low power level, the converters and DSPprocessor block 221 of the GSM transmitter 22 therefore provides acontrol signal to the tuning component 217. Thereupon, the tuningcomponent 217 detunes the GPS antenna 216 to somewhat lower or higherfrequencies. The resulting shifted GPS antenna frequency response isdepicted as third curve in FIG. 3 in the case the frequency is tuned toa lower frequency.

With the shifted GPS antenna frequency response, the antenna isolationbetween the GSM antenna 226 and the GPS antenna 216 is improved, asindicated by a double headed arrow in FIG. 3. When a GPS signal reachingthe mobile phone 20 is strong, and has thus a rather high SNR in spiteof the superimposed wideband noise, the signal received via the GPSantenna 216 may be strong enough for a detection even though the GPSantenna 216 is detuned. When a GPS signal reaching the mobile phone 20is weak, however, and has thus a rather low SNR due to the superimposedgenerated wideband noise, the signal received via the GPS antenna 216 isnot strong enough for a detection, and thus errors in the evaluation inthe converters and DSP processor block 214 are prevented. Therefore, theincreased attenuation between the GSM antenna 226 and the GPS antenna216 that the GSM transmitter 22 eases the performance degradation of theGPS receiver 21.

It is also possible to relate the amount of detuning to the extend ofthe respective amplification applied by GSM transmitter 22 to signalswhich are to be transmitted.

A second and a third embodiment of the invention, which will bepresented further below, take into account planned future developmentsof GPS.

The second embodiment of the invention is based on the assumption thatin addition to the C/A-code of the L1 signal, also the P-code of the L1signal and the L2 signal including a C/A code and a P-code are takeninto civil usage.

FIG. 4 is a schematic block diagram of a mobile phone 40, in which thesecond embodiment of the invention is implemented. As in FIG. 2, onlyselected components of the mobile phone 40 are depicted.

The mobile phone 40 of FIG. 4 supports again a GPS positioning and amobile communication via a GSM network. For supporting a GPSpositioning, the mobile phone 40 of FIG. 4 comprises a GPS receiver 41.The GPS receiver 41 includes a first receiving chain 43 for receivingand processing L1 signals and a second receiving chain 44 for receivingand processing L2 signals. The L1 receiving chain 43 comprises,connected to each other in series, a first low noise amplifier LNA 431,a first mixer 432 and a first variable gain attenuator 433. The L1receiving chain 43 further comprises a first local oscillator 435, whichis connected to the first mixer 432. The first local oscillator providesa signal having a frequency which is required for downconverting an L1signal. The L2 receiving chain 44 comprises, connected to each other inseries, a second low noise amplifier LNA 441, a second mixer 442 and asecond variable gain attenuator 443. The L2 receiving chain 44 furthercomprises a second local oscillator 445, which is connected to thesecond mixer 442. The second local oscillator 445 provides a signalhaving a frequency which is required for downconverting an L2 signal.The GPS receiver 41 comprises in addition a converters and DSP processorblock 414. The first variable gain attenuator 433 of the L1 receivingchain 43 and the second variable gain attenuator 443 of the L2 receivingchain 44 are both connected to this converters and DSP processor block414.

For supporting a GPS positioning, the mobile phone 40 moreover comprisesa GPS antenna 416. The GPS antenna 416 is connected by means of anenhanced diplexer 417 on the one hand to the first low noise amplifier431 of the L1 receiving chain 43 and on the other hand via a switch 418to the second low noise amplifier 44 of the L2 receiving chain 44.Typically, a diplexer combines two input path signals having differentfrequencies to one output path signal. The enhanced diplexer 417comprises a detuning circuitry and diplexer functionalities. Thedetuning function can be done with a capacitance diode or any othersuitable component. The detuning circuitry tunes the frequency band,which can be received via the GPS antenna 416.

For supporting a mobile communication, the mobile phone 40 comprises aGSM1800 transmitter 42, which is part of a GSM1800 transceiver. Thetransmitter 42 comprises a converters and DSP processor block 421, afirst variable power amplifier 422, a mixer 423 and a second variablepower amplifier 424. The transmitter 42 further comprises a localoscillator 425 which is connected to the mixer 423. The mobile phone 40further comprises a GSM antenna 426, which is connected to the secondvariable amplifier 424. The converters and DSP processor block 421 hasin addition a controlling access to the diplexer 417 and the switch 418.

For supporting a mobile communication, the mobile phone 40 may comprisein addition a GSM900 transmitter (not shown), which is part of a GSM900transceiver and designed similarly as the GSM1800 transmitter.

Transmissions via the GSM1800 transmitter and a GSM900 transmitter takeplace as described above with reference to FIG. 2 for the GSM1800transmitter.

While the GSM1800 transmitter 42 is not transmitting any signals, theGPS antenna 426 is connected via the diplexer 417 only to the L1receiver chain 43. The GPS antenna 416 is in resonance at the centerfrequency of the L1 frequency band, and received L1 signals areforwarded to the L1 receiver chain 43 and processed as described abovewith reference to FIG. 2.

When the GSM1800 transmitter 42 is transmitting signals, wideband noiseis generated in the L1 frequency band. The converters and DSP processorblock 421 therefore provides a control signal to the switch 418, whichcauses the switch 418 to be closed. As a result, signals received by theGPS antenna 416 are provided to both, the L1 and the L2 receiving chain43, 44. At the same time, the converters and DSP processor block 421provides a control signal to the diplexer 417, which causes the detuningcircuitry in the diplexer 417 to detune the GPS antenna 416 to be inresonance at the center frequency of the L2 frequency band.

The shift of the GPS antenna frequency response is illustrated in FIG.5. FIG. 5 is a diagram which corresponds to the diagram of FIG. 3,except that here, the GPS antenna frequency response was shifted exactlyto the L2 frequency band. The resulting improvement of the isolationbetween the GPS antenna 416 and the GSM antenna 426 is rather high, asindicated by a double-headed arrow in FIG. 5.

Due to the specific detuning in the second embodiment of the invention,a good reception of the L2 frequency band by the GPS antenna 416 andthus a good reception of the L2 band C/A and P-code in the L2 receivingchain 44 is achieved. From the L1 band, the C/A-code and the P-code canstill be received in some conditions via the L1 receiving chain 43, thatis, if the L1 signal reaching the mobile phone is particularly strong.In case of a strong L1 carrier signal, also the SNR of the L1 signalwill be sufficiently strong for an evaluation in spite of the widebandnoise.

FIGS. 6 a and 6 b illustrate the detuning in another type ofrepresentation. In FIG. 6 a, the insertion loss S₁₁ in dB of the GPSantenna 416 is depicted over the frequency for the case that there is noGSM1800 transmission. It can be seen that the insertion loss S₁₁ is ingeneral at a basically constant, high value, but decreases to a minimumvalue at a center frequency of 1575 MHz with a transition range on bothsides of this center frequency. This enables a good reception of the L1band C/A-code and the L1 band P-code in the L1 receiver chain 43. The L2receiver chain 44 is not in use. The GSM1800 transceiver may receivesignals at the same time, and if the mobile phone 40 comprises inaddition a GSM900 transceiver, the GSM900 transceiver may receive ortransmit signals at the same time, as such operations do not generateany wideband noise in the L1 frequency band.

In FIG. 6 b, the insertion loss S₁₁ in dB of the GPS antenna 416 isdepicted over the frequency for the case that there is an ongoingGSM1800 transmission. It can be seen that the insertion loss S₁₁ is ingeneral at a basically constant, high value, but decreases to a minimumvalue at a shifted center frequency of 1227 MHz with a transition rangeon both sides of this center frequency. This enables a good reception ofthe L2 band P-code in the L2 receiver chain 44. At the same time, thewideband noise generated by the GSM1800 transmission is attenuated.

The same result as for the European bands GSM1800 and GSM900 depicted inFIGS. 6 a and 6 b can be achieved for the U.S. bands GSM1900 and GSM850.

The third embodiment of the invention is based on the assumption that inaddition to the C/A-code of the L1 signal, also the P-code of the L1signal and of the L2 signal and a newly introduced C/A-code of the L2signal are taken into civil usage.

FIG. 7 is a schematic block diagram of a mobile phone 70, in which thethird embodiment of the invention is implemented. As in FIGS. 2 and 4,only selected components of the mobile phone 70 are depicted.

The mobile phone 70 of FIG. 7 supports again a GPS positioning and amobile communication via a GSM network. The C/A-code and the P-code ofthe L2 band are made use of in the GPS positioning for a diversityreception improvement.

The design of the mobile phone 70 of FIG. 7 is very similar to thedesign of the mobile phone of FIG. 4.

For supporting a GPS positioning, the mobile phone 70 of FIG. 7 thuscomprises a GPS receiver 71. The GPS receiver 71 includes a firstreceiving chain 73 for receiving and processing L1 signals and a secondreceiving chain 74 for receiving and processing L2 signals. The L1receiving chain 73 comprises, connected to each other in series, a firstlow noise amplifier LNA 731, a first mixer 732 and a first variable gainattenuator 733. The L1 receiving chain 73 further comprises a firstlocal oscillator 735, which is connected to the first mixer 732. Thefirst local oscillator provides a signal having a frequency which isrequired for downconverting an L1 signal. The L2 receiving chain 74comprises, connected to each other in series, a second low noiseamplifier LNA 741, a second mixer 742 and a second variable gainattenuator 743. The L2 receiving chain 74 further comprises a secondlocal oscillator 745, which is connected to the second mixer 742. Thesecond local oscillator 745 provides a signal having a frequency whichis required for downconverting an L2 signal. The GPS receiver 41comprises in addition a converters and DSP processor block 714. Thefirst variable gain attenuator 733 of the L1 receiving chain 73 and thesecond variable gain attenuator 743 of the L2 receiving chain 74 areboth connected to this converters and DSP processor block 714.

For supporting a GPS positioning, the mobile phone 70 moreover comprisesa first GPS antenna 716 and a second GPS antenna 719. The first GPSantenna 716 is connected by means of an enhanced diplexer 717 on the onehand to the first low noise amplifier 731 of the L1 receiving chain 73and on the other hand via a switch 718 to the second low noise amplifier741 of the L2 receiving chain 74. The enhanced diplexer 717 comprises adetuning circuitry for tuning the frequency band which can be receivedvia the first GPS antenna 716 from the L1 frequency band to the L2frequency band. The second GPS antenna 719 is connected equally via theswitch 718 to the second low noise amplifier 741 of the L2 receivingchain 74. The second GPS antenna 719 is tuned in a fixed manner to theL2 frequency band. The switch 718 allows to connect either the first GPSantenna 716 or the second GPS antenna 719 to the second GPS receivingchain 74.

For supporting a mobile communication, the mobile phone 70 comprises aGSM1900 transmitter 72, which is part of a GSM1900 transceiver. Thetransmitter 72 comprises a converters and DSP processor block 721, afirst variable power amplifier 722, a mixer 723 and a second variablepower amplifier 724. The transmitter 72 further comprises a localoscillator 725 which is connected to the mixer 723. The mobile phone 70further comprises a GSM antenna 726, which is connected to the secondvariable amplifier 724. The converters and DSP processor block 721 hasin addition a controlling access to the diplexer 717 and the switch 718.

For supporting a mobile communication, the mobile phone 70 comprises inaddition a GSM850 transmitter (not shown), which is part of a GSM850transceiver and designed similarly as the GSM1900 transmitter.

Transmissions via the GSM1900 transmitter 72 or the GSM850 transmitterare carried out as described above with reference to FIG. 2 for theGSM1800 transmitter 22, only in other frequency bands.

While neither the GSM1900 transmitter 72 nor the GSM850 transmitter istransmitting signals, the first GPS antenna 716 is connected via thediplexer 717 only to the first GPS receiver chain 73. At the same time,the second GPS antenna 719 is connected via the switch 71 8 to thesecond GPS receiver chain 74. The first GPS antenna 716 is in resonanceat the L1 frequency band, and received L1 signals are forwarded to-thefirst GPS receiver chain 73 and processed analogously as described abovewith reference to FIG. 2. The second GPS antenna 719 is in resonance atthe L2 frequency band, and received L2 signals are forwarded to thesecond GPS receiver 74 chain and processed analogously as describedabove with reference to FIG. 2. The GSM1800 transceiver and the GSM900transceiver may be receiving signals at the same time.

This first situation is illustrated in FIG. 8 a, in which the insertionloss S₁₁ in dB of both GPS antennas 716, 719 is depicted over thefrequency for the case that there is no GSM transmission. At the firstGPS antenna 716, the insertion loss S₁₁ is in general at a basicallyconstant, high value, but decreases to a minimum value at a centerfrequency of 1575 MHz with a transition range on both sides of thiscenter frequency. This enables a good reception of the L1 band C/A-codeand P-code via the first GPS antenna 716 in the first GPS receivingchain 73. At the second GPS antenna 719, the insertion loss S₁₁ is ingeneral at a basically constant, high value, but decreases to a minimumvalue at a center frequency of 1227 MHz with a transition range on bothsides of this center frequency. This enables a good reception of the L2band C/A-code and P-code via the second GPS antenna 719 in the secondGPS receiving chain 74.

When the GSM1900 transmitter 74 is transmitting signals, wideband noiseis generated in the L1 frequency band. The converters and DSP processorblock 721 therefore provides control signal to the switch 718, whichcauses the switch 718 to connect the diplexer 717 instead of the secondGPS antenna 719 to the second GPS receiving chain 74. Thereby, signalsreceived by the first GPS antenna 716 are provided to both, the firstand the second GPS receiving chain 73, 74. The second GPS antenna 719 isnow disconnected. At the same time, the converters and DSP processorblock 721 causes the first GPS antenna 716 to be detuned to be inresonance at the L2 frequency band.

This second situation is illustrated in FIG. 8 b, in which the insertionloss of the first GPS antenna 716 is depicted over the frequency for thecase that there is a GSM1900 transmission. At the first GPS antenna 716,the insertion loss S₁₁ is in general at a basically constant, highvalue, but decreases to a minimum value at a shifted center frequency of1227 MHz with a transition range on both sides of this center frequency.This enables a good reception of the L2 band C/A-code and P-code via thefirst GPS antenna 716 in the second GPS receiving chain 74. The widebandnoise generated by the GSM1900 transmission is thus attenuated. From theL1 band, the C/A-code and the P-code can be received in some conditionsvia the first GPS antenna 716 in the first GPS receiving chain 73, thatis, if the L1 satellite signal reaching the mobile phone 70 isparticularly strong. The disconnected second GPS antenna 719 does notforward any signals.

When the GSM850 transmitter is transmitting signals, wideband noise isgenerated in the L2 frequency band. The converters and DSP processorblock (not shown) of the GSM850 transmitter therefore provides a controlsignal to the switch 718, which causes the switch 718 to connect thediplexer 717 instead of the second GPS antenna 719 to the second GPSreceiving chain 74. Thereby, signals received by the first GPS antenna716 are provided to both, the first and the second GPS receiving chain73, 74. The second GPS-antenna 719 is now disconnected. The firstantenna is kept to be tuned to be in resonance at the L1 frequency band.

This third situation is illustrated in FIG. 8 c, in which the insertionloss S₁₁ of the first GPS antenna 716 is depicted over the frequency forthe case that there is a GSM850 transmission. At the first GPS antenna716, the insertion loss S₁₁ is in general at a basically constant, highvalue, but decreases to a minimum value at a center frequency of 1575MHz with a transition range on both sides of this center frequency. Thisenables a good reception of the L1 band C/A-code and P-code via thefirst GPS antenna 716 in the second GPS receiving chain 74. Thedisconnected second GPS antenna 719 does not forward any signals. Thewideband noise generated by the GSM850 transmission is thus attenuated.From the L2 band, the C/A-code and the P-code can be received in someconditions via the first GPS antenna 716 in the second GPS receivingchain 73, that is, if the L2 satellite signal reaching the mobile phone70 is particularly strong.

It is to be understood that in the second and third embodiment, one ofthe GPS receiver chains or an additional GPS receiver chain could alsobe a receiver chain for receiving GPS signals at the L5 band, ifsuitable signals are transmitted at this band.

It is further to be noted that the described embodiments constitute onlythree of a variety of possible embodiments of the invention.

1. Device (20,40,70) comprising: a receiver (21,41,71) comprising atleast a first receiving chain (43, 63) for receiving and processingradio frequency signals in a first frequency band and a second receivingchain (44,74) for receiving and processing radio frequency signals in asecond frequency band; at least a first antenna (216,416,716) which isconnected to said first receiving chain (43, 63) and in addition via aswitching component (418,718) to said second receiving chain (44,74); atuning component (217,417,717) for shifting a frequency response of saidfirst antenna (216,416,716) from said first frequency band to a secondfrequency band; and a controlling portion (221, 415, 715) causing saidtuning component (217,417,717) to shift said frequency response of saidfirst antenna (216,416,716) from said first frequency band to saidsecond frequency band and causing said switching component (418,718) toconnect said first antenna (416,716) to said second receiving chain(44,74), in case a wideband noise is expected in said first frequencyband.
 2. Device (20,40,70) according to claim 1, further comprising acommunication system transmitter (22,42,72) for transmitting signals viaa radio interface, wherein a transmission of signals by saidcommunication system transmitter (22,42,72) causes wideband noise insaid first frequency band, and wherein wideband noise in said firstfrequency band is expected by said controlling portion (221, 415, 715)whenever said communication system transmitter (22,42,72) istransmitting signals causing wideband noise in said first frequencyband.
 3. Device (70) according to claim 1, further comprising a secondantenna (719), which second antenna (719) has a frequency response atsaid second frequency band and which second antenna (719) is equallyconnected via said switching component (718) to said second receivingchain (74), wherein said controlling portion (715) causes said switchingcomponent (718) to disconnect said second antenna (719) from said secondreceiving chain (74), in case a wideband noise is expected in said firstfrequency band.
 4. Device (70) according to claim 3, wherein saidcontrolling portion (715) causes said switching component (718) toconnect said first antenna (716) to said second receiving chain (74) andto disconnect said second antenna (719) from said second receiving chain(74), in case a wideband noise is expected in said second frequencyband.
 5. Device (70) according to claim 4, further comprising acommunication system transmitter for transmitting signals via a radiointerface, wherein a transmission of signals by said communicationsystem transmitter causes wideband noise in said second frequency band,and wherein wideband noise in said second frequency band is expected bysaid controlling portion (715) whenever said communication systemtransmitter is transmitting signals causing wideband noise in saidsecond frequency band.
 6. Device (20,40,70) according to claim 1,wherein said receiver (21,41,71) is a Global Positioning System receiverfor receiving and processing Global Positioning System signalstransmitted by Global Positioning System satellites.
 7. Device (40,70)according to claim 6, wherein said first frequency band is a GlobalPositioning System L1 band and wherein said second frequency band is oneof a Global Positioning System L2 band and a Global Positioning SystemL5 band.
 8. Method for improving the performance of a receiver(21,41,71), which receiver (21,41,71) comprises at least a firstreceiving chain (43, 63) for receiving and processing radio frequencysignals in a first frequency band and a second receiving chain (44,74)for receiving and processing radio frequency signals in a secondfrequency band, wherein at least a first antenna (216,416,716) isconnected to said first receiving chain (43, 63) and in addition via aswitching component (418,718) to said second receiving chain (44,74),said method comprising: determining whether a wideband noise is expectedin said first frequency band; and shifting a frequency response of saidfirst antenna (216,416,716) from said first frequency band to a secondfrequency band and causing said switching component (418,718) to connectsaid first antenna (416,716) to said second receiving chain (44,74), incase a wideband noise is determined to be expected in said firstfrequency band.
 9. Method according to claim 8, wherein said receiver(21,41,71) is comprised in a single device (20,40,70) with acommunication system transmitter (22,42,72), a transmission of signalsby said communication system transmitter (22,42,72) causing widebandnoise in said first frequency band, and wherein determining whether awideband noise is expected in said first frequency band comprisesdetecting whether said communication system transmitter (22,42,72) istransmitting signals via a radio interface.
 10. Method according toclaim 8, wherein a second antenna (719) is connected to said receiver(71), which second antenna (719) has a frequency response at said secondfrequency band, said method further comprising preventing a processingof radio frequency signals received via said second antenna (719), incase a wideband noise is determined to be expected in said firstfrequency band.
 11. Method according to claim 10, further comprising:determining whether a wideband noise is expected in said secondfrequency band; enabling radio frequency signals in said secondfrequency band received via said first antenna (716) to be processed bysaid receiver (71), in case a wideband noise is determined to beexpected in said second frequency band; and preventing a processing ofradio frequency signals received via said second antenna (719) by saidreceiver (71), in case a wideband noise is determined to be expected insaid second frequency band.
 12. Method according to claim 11, whereinsaid receiver (71) is comprised in a single device (70) with acommunication system transmitter, wherein a transmission of signals bysaid communication system transmitter causes wideband noise in saidsecond frequency band, and wherein determining whether a wideband noiseis expected in said second frequency band comprises detecting whethersaid communication system transmitter is transmitting signals via aradio interface.
 13. Method according to claim 8, wherein said receiver(21,41,71) is a Global Positioning System receiver for receiving andprocessing Global Positioning System signals transmitted by GlobalPositioning System satellites.
 14. Method according to claim 13, whereinsaid first frequency band is a Global Positioning System L1 band andwherein said second frequency band is one of a Global Positioning SystemL2 band and a Global Positioning System L5 band.
 15. Mobile telephonewith global positioning system (GPS) receiver capability, comprising: areceiver having an antenna for receiving and a processor for processingGPS signals received at least in a first frequency band; a tuningcomponent responsive to a control signal for shifting a frequencyresponse of said antenna from said first frequency band to a secondfrequency band; and a control responsive to operation of said telephoneacting as a radio transmitter for providing said control signal.